Is there a link between exercise and happiness?

Just as antibody production is connected to both exercise and happiness, so too is endorphin production. Endorphins are chemicals that are able to cross through the gaps between neurons in order to pass along a message from one to the next. There are many different kinds, and much remains to be learned about their different purposes and functions.

One thing is known for certain about endorphins: their ability to make you feel oh-so-good. When your body is subjected to certain stimuli like sex, food or pain, your hypothalamus calls for endorphins, and the cells throughout your body that contain them heed the call. When endorphins lock into special receptor cells (called opioid receptors, because opiates also fit them), they block the transmission of pain signals and also produce a euphoric feeling -- exactly like opiates.

Endorphins act as both a painkiller and as the pay-off for your body's reward system. When you hurt yourself (or eat a hot chili pepper), you may get a big dose of endorphins to ease the pain. You may also get an endorphin blast from talking to a stranger, eating a satisfying meal or being exposed to ultraviolet light. (Everyone has different amounts of endorphins, and what may trigger an endorphin rush for one person could very well produce a dud for someone else.) The pay-off in the form of your body tapping into its own stash of "opiates" is to let you know you've had enough -- and convince you to do it again sometime soon.

Exercise stimulates endorphin production as well, but for a different reason. You're probably familiar with the term "runner's high," which refers to the euphoric feeling one sometimes gets when exercising. Researchers have found that light-to-moderate weight training or cardiovascular exercise doesn't produce endorphins, only heavy weights or training that incorporates sprinting or other anaerobic exertion.

When your body crosses over from an aerobic state to an anaerobic state, it's suddenly operating without enough oxygen to satisfy the muscles and cells screaming out for it. This is when the "runner's high" occurs.

Want more happiness articles? On the next page, find out how many calories you burn when you laugh -- and what science has to say about what makes you happy.